class People {
    constructor(name, house) {
        this.name = name;
        this.house = house;
    }
    saySomething() {}
}

class A extends People {
    constructor(name, house) {
        super(name, house);
    }
    saySomething() {
        alert('I am A')
    }
}

class B extends People {
    constructor(name, house) {
        super(name, house);
    }
    saySomething() {
        alert('I am B')
    }
}

class House {
    constructor(city) {
        this.city = city
    }
    showCity() {
        alert('beijing')
    }
}